Integrated circuit chips, such as micro-processor chips, and other electronic components generate heat during operation. These components are generally mounted on printed circuit boards (PCBs). To help ensure proper operation, these components generally are kept at an operating temperature below around 160° F. This means that cooling of some sort must be provided for proper operation of electronic components.
As one example, cold plates are widely used for cooling PCBs where the coolant must be kept separated from the electronic components, such as PCBs used in avionics units on aircraft. Avionics cooling on aircraft is commonly provided by blowing cooled, conditioned air through cold plate heat sinks that are attached to the back sides of PCBs (that is, the side away from the upper case of the chip). A cold plate generally consists of an enhanced heat transfer surface encapsulated in a high aspect ratio rectangular duct. The enhanced heat transfer surfaces are typically some sort of fin arrangement or an open-celled, porous metal foam. Coolant flows through the cold plate from one end to the other end, completely wetting the enhanced heat transfer surface inside. This system cools PCBs mounted to the sides of the cold plate.
Commercial Off-The-Shelf (COTS) chips are designed to dissipate the heat they generate through the upper case of the chip. Therefore, such chips are best cooled by direct cooling of the chip case. Adequate cooling of these chips is not easily achieved by back side cooling, such as by blowing cooled, conditioned air through cold plates attached to the back side of the PCB away from the chip upper case. Because back side cooling of COTS chips is not thermally efficient, COTS chips have historically been used sparingly in military aerospace applications. However, modern military aerospace designs emphasize use of COTS chips as a cost saving measure. Additionally, future commercial aerospace and non-aerospace designs employing such chips will require higher capacity, direct case cooling methods because they are projected to generate significantly more heat than contemporary chips while still having an operating temperature limit of around 160° F.
Research has been conducted on increasing the cooling capacity of direct case cooling designs by increasing the surface area wetted by coolant. This work has centered on increasing the heat transfer area available for cooling the case by attaching fins or foam to the chip case. Machined microchannel fin and pin fin arrays as well as metal foam designs have been tested. However, machined microchannel fin and pin fin arrays involve complicated and expensive manufacturing methods. Typical methods for generating chip surface microchannels include photolithography, plasma etching, and photochemical machining. Furthermore, only a single row of microchannels can be created on the chip surface. Multiple rows cannot be stacked on top of each other, thereby greatly reducing the area available for heat transfer and the amount of cooling air that can be utilized for heat removal. Metal foams are limited as to how much the heat transfer surface area can be increased.
Machined microchannel fin, pin fin array and metal foam chip case cooling systems are also only attached to the top surface of electronic component cases. This constitutes a further limit on the area available for heat transfer from a chip case. Attaching fin designs to both the top and sides of a chip case and then getting coolant to flow in a controlled manner over all the fins would be a difficult, costly design problem to solve. Metal foam could be machined to conform to a chip case, but it would be expensive. Furthermore, the outer surface of the foam would have to be sealed using an expensive, complex brazing or welding process.
It would be desirable to improve the thermal efficiency of direct case chip cooling by employing a design having a larger internal surface area available for heat transfer than existing designs, and that could be inexpensively manufactured and easily machined to fit conformally over the top and sides of a chip case. Such an improved approach to chip cooling could enable the wide use of COTS chips in aerospace applications and could enable higher-powered computer chips to be utilized in commercial aerospace and non-aerospace applications.
Specifically for aerospace applications, more thermally efficient chip case cooling designs would be attractive because the cooling air would commonly be generated by an aircraft environmental control system (ECS). However, generation of this cooling air by an ECS constitutes a system performance penalty for the aircraft, because the ECS generates cooling air by extracting air from the aircraft's engine and cooling it with ram air ducted into the vehicle from outside. Extracting air from the engine reduces the air available for generating thrust while capturing ram air increases aircraft drag. These effects ultimately reduce range and/or payload for an aircraft.
Therefore, it would be desirable to reduce the amount of air required to cool avionics chips, thereby reducing the system performance penalty for an air vehicle by increasing vehicle thrust and/or lowering fuel consumption. It would also be desirable to address cooling of future high power electronics that are projected to generate significantly more heat than contemporary chips while still having an operating temperature limit of around 160° F. This will require making more efficient use of the cooling air available.
The foregoing examples of related art and limitations associated therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.